Linear nozzles for electrostatic deposition have been used to apply nonconductive materials to a target (substrate). Typically, these substrates consist of dimensions exceeding several inches. In some coated products, the substrate is much smaller than a span of several inches. Single point nozzles greatly improved the ability to apply highly charged material to smaller objects with the same precise control as a linear nozzle.
As more demanding material applications are presented, the need for more precision and consistency in spraying smaller objects becomes a priority. In using a single point nozzle, there are many physical variables that are difficult to control. One challenge in using a single point nozzle is using low flow rates. At low flow rates, the evaporative characteristics of the fluid become very important, as sealing issues create inconsistent viscosities and therefore, poorer process control.
Many single point nozzles are manufactured using split-half construction, which allows for leakage or blockage of the fluid passage. Sealing is necessary when solvented materials are applied, but persistent small leakages between the split-halves causes uncontrollable increases in concentrations of the fluid being deposited. Current materials in constructing a single point nozzle, including acetal or polyether ether ketone (PEEK), are difficult to machine at the precise levels needed for a consistent nozzle tip. With a split design, it is difficult to align the halves and maintain consistency in the spraying.
The sharpness and symmetry of the tip is critical to the formation of the most optimal meniscus and the lowest firing voltage. Using current materials and construction methods, durability and consistent symmetry of the tip is a challenge. Further, a thin electrode is often positioned between the split-halves and makes for an additional component to properly align between uses and after cleaning.